Analyses of spacer grids compression strength and fuel assemblies structural behavior

• Modeling of a 16 × 16 spacer grid to reproduce compression tests.
• Evaluation of spacer grids mechanical behavior.
• Modeling of fuel assembly with beam-type finite elements.
• Calculation of fuel assembly natural frequencies by considering fuel rods sliding.
• A new procedure to correct fuel assembly natural frequencies with weighting factor β.

In this work, finite-element models were proposed to evaluate the spacer grids compression strength and structural behavior of fuel assemblies, mainly in terms of their natural frequencies. Firstly, a three-dimensional model was developed to provide consistent predictions of 16 × 16-type spacer grids compression strength. Regarding their original geometry and some possible design variations, the models were submitted to compression conditions to calculate the maximum compression force and they were validated for comparison with experimental predictions. Secondly, fuel assembly models were proposed with the aim at to correct its natural frequencies. For that, two distinct three-dimensional finite element approaches for the spacer grids, called total mesh and inner mesh, were adopted, respectively. For each model, the maximum and minimum fuel assembly lateral stiffness was determined. Also, by adopting the correction factor β, the natural frequencies were corrected by a β value that was characteristic of each model and compared to experimental results. The procedure used in the present work permitted a good agreement between numerical and experimental natural frequencies results with the total mesh model.